Dosage forms manufactured as a compressed, single-layer tablet comprising a cellulose polymer and a racemic drug mixture are known to the drug dispensing art. For example, such a single-layered dosage form is disclosed in the following references: U.S. Pat. No. 3,870,790 issued to Lowey et al; U.S. Pat. No. 4,140,755 issued to Sheth et al; U.S. Pat. No. 4,167,558 issued to Sheth et al; U.S. Pat. No. 4,226,849 issued to Schor; U.S. Pat. No. 4,259,314 issued to Lowey; U.S. Pat. No. 4,357,469 issued to Schor; U.S. Pat. No. 4,369,172 issued to Schor et al; U.S. Pat. No. 4,389,393 issued to Schor et al; U.S. Pat. No. 4,540,566 issued to Davis et al; U.S. Pat. No. 4,571,333 issued to Hsiao et al; U.S. Pat. No. 4,680,323 issued to Lowey; and U.S. Pat. No. 4,849,229 issued to Gaylord et al. A dosage form manufactured as a bilayered tablet comprising a cellulose polymer and a racemic drug mixture is disclosed in the following references: U.S. Pat. No. 4,786,503 issued to Edgren et al; and U.S. Pat. No. 4,946,685 issued to Edgren et al.
While the dosage forms known to the prior art provide for delivering a racemic drug mixture, they do not provide for delivering a single, stereoisomer drug. Stereoisomers are molecules comprising atoms uniquely oriented in space. Stereoisomers as compounds were first discovered by a mineralogist named Biot in 1815. About 30 years later, Pasteur observed that certain stereoisomers, called optical isomers, had a mirror-image relationship. Thirty years passed from then until a theory was proposed by van't Hoff and LeBel to account for the optical activity of such compounds, based on the asymmetrical bonding around a carbon atom. Fifty years then passed before systematic studies were reported by Cushny on the pharmacological effects of some naturally occurring optical isomers. About 10 years later, in 1933, Easson and Stedman proposed a hypothesis to account for differences between effects of optical isomers. Since then, attention has been given to the role of spatial configuration in the effects of drugs. The stereoisomer drug generally differs in increased pharmacodynamic and pharmacokinetic properties attributed to drugs stereoselective interaction with the biological macromolecules, as reported in Handbook of Stereoisomers, by Smith, page 1, (1989), published by CRC Press, Inc., Boca Raton, Fla., and in J. Pharmaceutical Sciences, Vol. 78, page 695, (1989).
The dosage forms known to the above prior art for delivering a racemic drug mixture possess major shortcomings and they are in need of inventive improvement. For example, the prior art dosage forms deliver excess and unneeded drug as these forms deliver a racemic mixture of the drug and they do not provide for delivering the more physiologically-active stereoisomer of the drug. The prior art single layer dosage forms deliver the racemic mixture of the drug and these dosage forms lack the means for delivering independently the more active stereoisomer of the drug. Another shortcoming is the prior art bilayer form does not provide for immediate therapy at an enhanced level achieved by delivering the more active stereoisomer first, followed by the continuous and prolonged delivery of the drug racemate. Also, the prior art dosage forms do not provide that a drug molecule in its more physiologically active form can be delivered free of interaction with the dosage form to a biological, stereoselective drug receptor for quick and increased drug therapy.
In light of the above presentation, it will be appreciated by those versed in the dispensing art, that if a novel dosage form is made available to the medical, veterinary and pharmaceutical arts, that overcomes the shortcomings known to the prior art, such a dosage form would have a definite use and it would also be a valuable contribution to the dispensing art. It will be appreciated further by those versed in the dispensing art that if a dosage form can be provided that (a) possesses the ability to deliver a drug stereoisomer, followed by (b) the ability to deliver a racemate of the drug, and which dosage form (c) can be manufactured at an economical cost, such a dosage form would have a positive and practical value, and it would also represent an advancement in the pharmaceutical, medical and veterinary arts.